This invention relates to an apparatus for automatic fingerprint classification.
There are two types of processing fingerprint images for automatic fingerprint classification. In a first type of processing, a fingerprint image is subdivided in a plural number of subregions, and for each subregion, a ridge line direction is quantized, a core point of the fingerprint image is determined from quantized ridge line directions of subregions, and the fingerprint is classified in accordance with the shape and the direction trend of ridge line directions in an area near to the core point. This type of processing is disclosed, for example, in a U.S. Pat. No. 5,337,369.
In a second type of processing, ridge lines of a fingerprint are processed to produce a thin line in the center of each ridge line. This type of processing is disclosed, for example, in a Japanese patent application entitled "A method and an apparatus for fingerprint pattern detection" and laid open as a Provisional Publication No. 153687/'88, wherein thinned ridge lines are approximated by fragmental straight line segments. The fingerprint is classified in accordance with direction distribution of these straight line segments.
In these two types of processing, there are advantages and disadvantages. When a fingerprint is smudged, ridge line direction of a smudged subregion can not be determined, or it is mistakenly determined. This is a disadvantage of the first type of processing. And, in the method disclosed by tile Provisional Publication No. 153687/'88, the core point is not used for classification. This is a disadvantage of the second type processing, as ridge line directions in a neighborhood of the core point are most important for classification.